The subject invention pertains, in general, to rectifier circuits employing active solid state rectifying elements, or devices; and, in particular, to rectifier circuits employing transistors as rectifying elements, or devices. The subject invention pertains, more particularly, to the employment of transistors connected in an unusual arrangement and serving as rectifying elements, or devices.
There are many applications which require a small volume, lightweight, power supply unit including a rectifier. For example, such a power supply unit may be incorporated in a conventional two, or three, conductor line cord at one end of the cord and incorporated in a male plug adapted for connection with a wall receptacle which supplies a single phase, 60 Hertz source of 120 volts. The power supply unit converts, or changes, the supplied phase, frequency and voltage to suit the appliance(s) which are intended to be connected to the end of the cord. The described assembly is often called a line cord power supply. The power supply itself is a small, compact, lightweight unit which is usually integral with the line cord and is supported by the line cord.
The small volume, lightweight power supply unit, hereinbefore discussed, includes a rectifier. The rectifier must be of small volume and lightweight. Another important requirement respecting such rectifiers is that high efficiency rectification be achievable. Furthermore, rectifier operation should be stable for long periods of time even under adverse ambient temperatures and humidity. In addition, such rectifiers should be relatively inexpensive.
The aforementioned requirements have not been satisfactorily met in cases where such rectifiers are intended to operate at relatively low voltages, relatively high current and relatively high frequencies (e.g., 10 volts or less, up to several amperes and up to 50 kilohertz.) Known efforts employing such passive rectifying elements, or devices, as silicon diodes, Schottky diodes and germanium diodes have not proved satisfactory. For example, a simple, full-wave rectifier circuit using silicon diodes exhibits poor rectification efficiency where the load voltage is below 10 volts. The poor efficiency is due to the inherent forward voltage drop of the silicon junction which, for low cost diodes, is about 1 volt at 1 ampere when the silicon diodes are operating near their ratings. Also, additional power dissipation in the form of switching losses occurs due to high frequency operation; the high frequency being necessary for the employment of minimum volume magnetic components which are necessary in other parts of the rectifier circuit. As another example, high voltage Schottky (hot carrier) diodes are large area devices and are not suitable because, among other reasons, they are difficult to incorporate economically in integrated circuits. As a further example, germanium diodes are not generally suited for rectification at high frequencies. Moreover, germanium diodes are not suitable for integrated circuit fabrication.
The use of active devices, such as transistors, as rectifying elements is also known. See, for example, the article "New Techniques in Power Control" by J. B. Gunn, Digest of Technical Papers, 1970 IEEE International Solid State Circuit Conference, at pages 90 and 91. The rectifier circuit hereinafter disclosed in detail represents a departure from the rectifier circuit disclosed in the Gunn article.